Systems and methods for improved sustainment of a high performance frc with multi-scaled capture type vacuum pumping

ABSTRACT

Systems and methods that facilitate forming and maintaining FRCs with superior stability as well as particle, energy and flux confinement and, more particularly, systems and methods that facilitate forming and maintaining FRCs with elevated system energies and improved sustainment utilizing multi-scaled capture type vacuum pumping.

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject application is a continuation of U.S. Pat. Application No.17/521,449, filed Nov. 8, 2021, which is a continuation of U.S. Pat.Application No. 16/399,396, filed Apr. 30, 2019, now U.S. Pat. No.11,211,172, which is a continuation of International Patent ApplicationNo. PCT/US17/60255, filed Nov. 6, 2017, which claims priority to U.S.Provisional Pat. Application No. 62/418,119, filed on Nov. 4, 2016, allof which are incorporated by reference herein in their entireties forall purposes.

FIELD

The subject matter described herein relates generally to magnetic plasmaconfinement systems having a field reversed configuration (FRC) and,more particularly, more particularly, to systems and methods thatfacilitate forming and maintaining FRCs with elevated system energiesand improved sustainment utilizing multi-scaled capture type vacuumpumping.

BACKGROUND INFORMATION

The Field Reversed Configuration (FRC) belongs to the class of magneticplasma confinement topologies known as compact toroids (CT). It exhibitspredominantly poloidal magnetic fields and possesses zero or smallself-generated toroidal fields (see M. Tuszewski, Nucl. Fusion 28, 2033(1988)). The attractions of such a configuration are its simple geometryfor ease of construction and maintenance, a natural unrestricteddivertor for facilitating energy extraction and ash removal, and veryhigh β (β is the ratio of the average plasma pressure to the averagemagnetic field pressure inside the FRC), i.e., high power density. Thehigh β nature is advantageous for economic operation and for the use ofadvanced, aneutronic fuels such as D-He³ and p-B¹¹.

The traditional method of forming an FRC uses the field-reversed θ-pinchtechnology, producing hot, high-density plasmas (see A. L. Hoffman andJ. T. Slough, Nucl. Fusion 33, 27 (1993)). A variation on this is thetranslation-trapping method in which the plasma created in a theta-pinch“source” is more-or-less immediately ejected out one end into aconfinement chamber. The translating plasmoid is then trapped betweentwo strong mirrors at the ends of the chamber (see, for instance, H.Himura, S. Okada, S. Sugimoto, and S. Goto, Phys. Plasmas 2, 191(1995)). Once in the confinement chamber, various heating and currentdrive methods may be applied such as beam injection (neutral orneutralized), rotating magnetic fields, RF or ohmic heating, etc. Thisseparation of source and confinement functions offers key engineeringadvantages for potential future fusion reactors. FRCs have proved to beextremely robust, resilient to dynamic formation, translation, andviolent capture events. Moreover, they show a tendency to assume apreferred plasma state (see e.g. H. Y. Guo, A. L. Hoffman, K. E. Miller,and L. C. Steinhauer, Phys. Rev. Lett. 92, 245001 (2004)). Significantprogress has been made in the last decade developing other FRC formationmethods: merging spheromaks with oppositely-directed helicities (seee.g. Y. Ono, M. Inomoto, Y. Ueda, T. Matsuyama, and T. Okazaki, Nucl.Fusion 39, 2001 (1999)) and by driving current with rotating magneticfields (RMF) (see e.g. I. R. Jones, Phys. Plasmas 6, 1950 (1999)) whichalso provides additional stability.

Recently, the collision-merging technique, proposed long ago (see e.g.D. R. Wells, Phys. Fluids 9, 1010 (1966)) has been significantlydeveloped further: two separate theta-pinches at opposite ends of aconfinement chamber simultaneously generate two plasmoids and acceleratethe plasmoids toward each other at high speed; they then collide at thecenter of the confinement chamber and merge to form a compound FRC. Inthe construction and successful operation of one of the largest FRCexperiments to date, the conventional collision-merging method was shownto produce stable, long-lived, high-flux, high temperature FRCs (seee.g. M. Binderbauer, H.Y. Guo, M. Tuszewski et al., Phys. Rev. Lett.105, 045003 (2010)).

FRCs consist of a torus of closed field lines inside a separatrix, andof an annular edge layer on the open field lines just outside theseparatrix. The edge layer coalesces into jets beyond the FRC length,providing a natural divertor. The FRC topology coincides with that of aField-Reversed-Mirror plasma. However, a significant difference is thatthe FRC plasma has a β of about 10. The inherent low internal magneticfield provides for a certain indigenous kinetic particle population,i.e. particles with large larmor radii, comparable to the FRC minorradius. It is these strong kinetic effects that appear to at leastpartially contribute to the gross stability of past and present FRCs,such as those produced in the collision-merging experiment.

Typical past FRC experiments have been dominated by convective losseswith energy confinement largely determined by particle transport.Particles diffuse primarily radially out of the separatrix volume, andare then lost axially in the edge layer. Accordingly, FRC confinementdepends on the properties of both closed and open field line regions.The particle diffusion time out of the separatrix scales as τ_(⊥) ~a²/D_(⊥) (a ~ r_(s)/4, where r_(s) is the central separatrix radius),and D_(⊥) is a characteristic FRC diffusivity, such as D_(⊥) ~ 12.5ρ_(ie), with ρ_(ie) representing the ion gyroradius, evaluated at anexternally applied magnetic field. The edge layer particle confinementtime τ_(||) is essentially an axial transit time in past FRCexperiments. In steady-state, the balance between radial and axialparticle losses yields a separatrix density gradient length δ ~(D_(⊥)τ||)^(½). The FRC particle confinement time scales as(τ_(⊥)τ||)^(½) for past FRCs that have substantial density at theseparatrix (see e.g. M. Tuszewski, “Field Reversed Configurations,”Nucl. Fusion 28, 2033 (1988)).

In light of the foregoing, it is, therefore, desirable to improve thesustainment of FRCs in order to use steady state FRCs with elevatedenergy systems as a pathway to a reactor core for fusion of light nucleifor the future generation of energy.

SUMMARY

The present embodiments provided herein are directed to systems andmethods that facilitate forming and maintaining FRCs with elevatedsystem energies and improved sustainment utilizing multi-scaled capturetype vacuum pumping. According to an embodiment of the presentdisclosure, a method for generating and maintaining a magnetic fieldwith a field reversed configuration (FRC) comprising forming an FRCabout a plasma in a confinement chamber, injecting a plurality ofneutral beams into the FRC plasma at an angle toward the mid-plane ofthe confinement chamber, pumping neutralized gas molecules accumulatingin first and second diametrically opposed divertors coupled to theconfinement chamber with first and second capture vacuum pumpspositioned in the first and second divertors and comprising two or moresides with surfaces having a view of each other and an open side,wherein the first and second capture vacuum pumps having a stickingfactor more than four (4) times greater than a sticking factor of a flatplate defining an area equivalent to the open side of the first andsecond capture pumps.

According to a further embodiment of the present disclosure, at leastone of the two or more sides of the first and second capture vacuumpumps comprising an array of individual capture vacuum pumps.

According to a further embodiment of the present disclosure, each of theindividual capture vacuum pumps comprising two or more sides withsurfaces having a view of each other and an open side, wherein each ofthe individual capture vacuum pumps having a sticking factor greaterthan a sticking factor of a flat plate defining an area equivalent tothe open side of each of the individual capture vacuum pumps.

According to a further embodiment of the present disclosure, the firstand second capture vacuum pumps having a sticking factor that is N timesgreater than a sticking factor of a flat plate defining an areaequivalent to the open side of the first and second capture pumps,wherein N is 4<N<16.

According to a further embodiment of the present disclosure, thesurfaces of the flat plate and the first and second vacuum pumpsincludes a film of titanium deposited thereon.

According to a further embodiment of the present disclosure, the methodfurther comprising injecting compact toroid (CT) plasmas from first andsecond CT injectors into the FRC plasma at an angle towards themid-plane of the confinement chamber, wherein the first and second CTinjectors are diametrically opposed on opposing sides of the mid-planeof the confinement chamber.

According to a further embodiment of the present disclosure, a capturevacuum pump comprises two or more sides with surfaces having a view ofeach other and an open side, wherein capture vacuum pump having asticking factor more than four (4) times greater than a sticking factorof a flat plate defining an area equivalent to the open side of thecapture pump.

According to a further embodiment of the present disclosure, at leastone of the two or more sides of the first and second capture vacuumpumps comprising an array of individual capture vacuum pumps.

According to a further embodiment of the present disclosure, each of theindividual capture vacuum pumps comprising two or more sides withsurfaces having a view of each other and an open side, wherein each ofthe individual capture vacuum pumps having a sticking factor greaterthan a sticking factor of a flat plate defining an area equivalent tothe open side of each of the individual capture vacuum pumps.

According to a further embodiment of the present disclosure, the firstand second capture vacuum pumps having a sticking factor that is N timesgreater than a sticking factor of a flat plate defining an areaequivalent to the open side of the first and second capture pumps,wherein N is 4<N<16.

According to a further embodiment of the present disclosure, thesurfaces of the flat plate and the first and second vacuum pumpsincludes a film of titanium deposited thereon.

According to a further embodiment of the present disclosure, a systemfor generating and maintaining a magnetic field with a field reversedconfiguration (FRC) comprising a confinement chamber, first and seconddiametrically opposed FRC formation sections coupled to the confinementchamber and including first and second capture vacuum pumps positionedwithin the first and second divertors and comprising two or more sideswith surfaces having a view of each other and an open side, wherein thefirst and second capture vacuum pumps having a sticking factor more thanfour (4) times greater than a sticking factor of a flat plate definingan area equivalent to the open side of the first and second capturepumps, one or more of a plurality of plasma guns, one or more biasingelectrodes and first and second mirror plugs, wherein the plurality ofplasma guns includes first and second axial plasma guns operably coupledto the first and second divertors, the first and second formationsections and the confinement chamber, wherein the one or more biasingelectrodes being positioned within one or more of the confinementchamber, the first and second formation sections, and the first andsecond outer divertors, and wherein the first and second mirror plugsbeing position between the first and second formation sections and thefirst and second divertors, a gettering system coupled to theconfinement chamber and the first and second divertors, a plurality ofneutral atom beam injectors coupled to the confinement chamber andangled toward a mid-plane of the confinement chamber.

According to a further embodiment of the present disclosure, the systemfurther comprising first and second compact toroid (CT) injectorscoupled to the confinement chamber at an angle towards the mid-plane ofthe confinement chamber, wherein the first and second CT injectors arediametrically opposed on opposing sides of the mid-plane of theconfinement chamber.

The systems, methods, features and advantages of the example embodimentswill be or will become apparent to one with skill in the art uponexamination of the following figures and detailed description. It isintended that all such additional methods, features and advantages beincluded within this description, and be protected by the accompanyingclaims. It is also intended that the claims are not limited to requirethe details of the example embodiments.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings, which are included as part of the presentspecification, illustrate the presently example embodiments and,together with the general description given above and the detaileddescription of the example embodiments given below, serve to explain andteach the principles of the present invention.

FIG. 1 illustrates particle confinement in the present FRC system undera high performance FRC regime (HPF) versus under a conventional FRCregime (CR), and versus other conventional FRC experiments.

FIG. 2 illustrates the components of the present FRC system and themagnetic topology of an FRC producible in the present FRC system.

FIG. 3A illustrates the basic layout of the present FRC system as viewedfrom the top, including the preferred arrangement of the centralconfinement vessel, formation section, divertors, neutral beams,electrodes, plasma guns, mirror plugs and pellet injector.

FIG. 3B illustrates the central confinement vessel as viewed from thetop and showing the neutral beams arranged at an angle normal to themajor axis of symmetry in the central confinement vessel.

FIG. 3C illustrates the central confinement vessel as viewed from thetop and showing the neutral beams arranged at an angle less than normalto the major axis of symmetry in the central confinement vessel anddirected to inject particles toward the mid-plane of the centralconfinement vessel.

FIGS. 3D and 3E illustrate top and perspective views, respectively, ofthe basic layout of an alternative embodiment of the present FRC system,including the preferred arrangement of the central confinement vessel,formation section, inner and outer divertors, neutral beams arranged atan angle less than normal to the major axis of symmetry in the centralconfinement vessel, electrodes, plasma guns and mirror plugs.

FIG. 4 illustrates a schematic of the components of a pulsed powersystem for the formation sections.

FIG. 5 illustrates an isometric view of an individual pulsed powerformation skid.

FIG. 6 illustrates an isometric view of a formation tube assembly.

FIG. 7 illustrates a partial sectional isometric view of neutral beamsystem and key components.

FIG. 8 illustrates an isometric view of the neutral beam arrangement onconfinement chamber.

FIG. 9 illustrates a partial sectional isometric view of a preferredarrangement of the Ti and Li gettering systems.

FIG. 10 illustrates a partial sectional isometric view of a plasma guninstalled in the divertor chamber. Also shown are the associatedmagnetic mirror plug and a divertor electrode assembly.

FIG. 11 illustrates a preferred layout of an annular bias electrode atthe axial end of the confinement chamber.

FIG. 12 illustrates the evolution of the excluded flux radius in the FRCsystem obtained from a series of external diamagnetic loops at the twofield reversed theta pinch formation sections and magnetic probesembedded inside the central metal confinement chamber. Time is measuredfrom the instant of synchronized field reversal in the formationsources, and distance z is given relative to the axial midplane of themachine.

FIGS. 13A, 13B, 13C and 13D illustrate data from a representativenon-HPF, un-sustained discharge on the present FRC system. Shown asfunctions of time are (FIG. 13A) excluded flux radius at the midplane,(FIG. 13B) 6 chords of line-integrated density from the midplane CO2interferometer, (FIG. 13C) Abel-inverted density radial profiles fromthe CO2 interferometer data, and (FIG. 13D) total plasma temperaturefrom pressure balance.

FIG. 14 illustrates the excluded flux axial profiles at selected timesfor the same discharge of the present FRC system shown in FIGS. 13A,13B, 13C and 13D.

FIG. 15 illustrates an isometric view of the saddle coils mountedoutside of the confinement chamber.

FIGS. 16A, 16B, 16C and 16D illustrate the correlations of FRC lifetimeand pulse length of injected neutral beams. As shown, longer beam pulsesproduce longer lived FRCs.

FIGS. 17A, 17B, 17C and 17D illustrate the individual and combinedeffects of different components of the FRC system on FRC performance andthe attainment of the HPF regime.

FIGS. 18A, 18B, 18C and 18D illustrate data from a representative HPF,un-sustained discharge on the present FRC system. Shown as functions oftime are (FIG. 18A) excluded flux radius at the midplane, (FIG. 18B) 6chords of line-integrated density from the midplane CO2 interferometer,(FIG. 18C) Abel-inverted density radial profiles from the CO2interferometer data, and (FIG. 18D) total plasma temperature frompressure balance.

FIG. 19 illustrates flux confinement as a function of electrontemperature (T_(e)). It represents a graphical representation of a newlyestablished superior scaling regime for HPF discharges.

FIG. 20 illustrates the FRC lifetime corresponding to the pulse lengthof non-angled and angled injected neutral beams.

FIGS. 21A, 21B, 21C, 21D and 21E illustrate the pulse length of angledinjected neutral beams and the lifetime of FRC plasma parameters ofplasma radius, plasma density, plasma temperature, and magnetic fluxcorresponding to the pulse length of angled injected neutral beams.

FIGS. 22A and 22B illustrate the basic layout of a compact toroid (CT)injector.

FIGS. 23A and 23B illustrate the central confinement vessel showing theCT injector mounted thereto.

FIGS. 24A and 24B illustrate the basic layout of an alternativeembodiment of the CT injector having a drift tube coupled thereto.

FIG. 25 illustrates an isometric view of the FRC plasma core and theconfinement chamber DC coils, and the path of charged particles flowingfrom the FRC plasma core.

FIG. 26 illustrates an isometric view of a divertor.

FIG. 27 is a graph illustrating the density of neutral gas accumulatingin the inner and outer divertors as a function of time during operationof the present FRC system.

FIG. 28 illustrates an isometric view of an individual pump object inthe form of an open face cube and a flat plate equivalent in size to theopen face of the cube.

FIG. 29 is a graph illustrating the effective sticking factor of thesquare opening of a box shaped pump object as a function of thedepth/width ratio of the box for a given sticking factor for flatsurfaces that make up the box.

FIG. 30 illustrates an isometric view of a self-similar surfaced capturepump comprising an open sided cube formed from sides comprising an arrayof individual pumps comprising an open faced cube.

FIG. 31 is a graph illustrating the increase in effective stickingfactor of a self-similar surfaced capture pump as a function of discretescale levels of self-similarity.

FIG. 32 illustrates isometric detail views showing the scale levels ofself-similarity of a self-similar surfaced capture pump.

It should be noted that the figures are not necessarily drawn to scaleand that elements of similar structures or functions are generallyrepresented by like reference numerals for illustrative purposesthroughout the figures. It also should be noted that the figures areonly intended to facilitate the description of the various embodimentsdescribed herein. The figures do not necessarily describe every aspectof the teachings disclosed herein and do not limit the scope of theclaims.

DETAILED DESCRIPTION

The present embodiments provided herein are directed to systems andmethods that facilitate forming and maintaining FRCs with superiorstability as well as particle, energy and flux confinement. Some of thepresent embodiments are directed to systems and methods that facilitateforming and maintaining FRCs with improved sustainment utilizingmulti-scaled capture type vacuum pump.

Representative examples of the embodiments described herein, whichexamples utilize many of these additional features and teachings bothseparately and in combination, will now be described in further detailwith reference to the attached drawings. This detailed description ismerely intended to teach a person of skill in the art further detailsfor practicing preferred aspects of the present teachings and is notintended to limit the scope of the invention. Therefore, combinations offeatures and steps disclosed in the following detail description may notbe necessary to practice the invention in the broadest sense, and areinstead taught merely to particularly describe representative examplesof the present teachings.

Moreover, the various features of the representative examples and thedependent claims may be combined in ways that are not specifically andexplicitly enumerated in order to provide additional useful embodimentsof the present teachings. In addition, it is expressly noted that allfeatures disclosed in the description and/or the claims are intended tobe disclosed separately and independently from each other for thepurpose of original disclosure, as well as for the purpose ofrestricting the claimed subject matter independent of the compositionsof the features in the embodiments and/or the claims. It is alsoexpressly noted that all value ranges or indications of groups ofentities disclose every possible intermediate value or intermediateentity for the purpose of original disclosure, as well as for thepurpose of restricting the claimed subject matter.

Before turning to the systems and methods that facilitate sustainment anFRC plasma utilizing multi-scaled capture type vacuum pumping, adiscussion of systems and methods for forming and maintaining highperformance FRCs with superior stability as well as superior particle,energy and flux confinement over conventional FRCs is provided. Suchhigh performance FRCs provide a pathway to a whole variety ofapplications including compact neutron sources (for medical isotopeproduction, nuclear waste remediation, materials research, neutronradiography and tomography), compact photon sources (for chemicalproduction and processing), mass separation and enrichment systems, andreactor cores for fusion of light nuclei for the future generation ofenergy.

Various ancillary systems and operating modes have been explored toassess whether there is a superior confinement regime in FRCs. Theseefforts have led to breakthrough discoveries and the development of aHigh Performance FRC paradigm described herein. In accordance with thisnew paradigm, the present systems and methods combine a host of novelideas and means to dramatically improve FRC confinement as illustratedin FIG. 1 as well as provide stability control without negativeside-effects. As discussed in greater detail below, FIG. 1 depictsparticle confinement in an FRC system 10 described below (see FIGS. 2and 3 ), operating in accordance with a High Performance FRC regime(HPF) for forming and maintaining an FRC versus operating in accordancewith a conventional regime CR for forming and maintaining an FRC, andversus particle confinement in accordance with conventional regimes forforming and maintaining an FRC used in other experiments. The presentdisclosure will outline and detail the innovative individual componentsof the FRC system 10 and methods as well as their collective effects.

FRC System Vacuum System

FIGS. 2 and 3 depict a schematic of the present FRC system 10. The FRCsystem 10 includes a central confinement vessel 100 surrounded by twodiametrically opposed reversed-field-theta-pinch formation sections 200and, beyond the formation sections 200, two divertor chambers 300 tocontrol neutral density and impurity contamination. The present FRCsystem 10 was built to accommodate ultrahigh vacuum and operates attypical base pressures of 10⁻⁸ torr. Such vacuum pressures require theuse of double-pumped mating flanges between mating components, metalO-rings, high purity interior walls, as well as careful initial surfaceconditioning of all parts prior to assembly, such as physical andchemical cleaning followed by a 24 hour250° C. vacuum baking andHydrogen glow discharge cleaning.

The reversed-field-theta-pinch formation sections 200 are standardfield-reversed-theta-pinches (FRTPs), albeit with an advanced pulsedpower formation system discussed in detail below (see FIGS. 4 through 6). Each formation section 200 is made of standard opaque industrialgrade quartz tubes that feature a 2 millimeter inner lining of ultrapurequartz. The confinement chamber 100 is made of stainless steel to allowa multitude of radial and tangential ports; it also serves as a fluxconserver on the timescale of the experiments described below and limitsfast magnetic transients. Vacuums are created and maintained within theFRC system 10 with a set of dry scroll roughing pumps, turbo molecularpumps and cryo pumps.

Magnetic System

The magnetic system 400 is illustrated in FIGS. 2 and 3 . FIG. 2 ,amongst other features, illustrates an FRC magnetic flux and densitycontours (as functions of the radial and axial coordinates) pertainingto an FRC 450 producible by the FRC system 10. These contours wereobtained by a 2-D resistive Hall-MHD numerical simulation using codedeveloped to simulate systems and methods corresponding to the FRCsystem 10, and agree well with measured experimental data. As seen inFIG. 2 , the FRC 450 consists of a torus of closed field lines at theinterior 453 of the FRC 450 inside a separatrix 451, and of an annularedge layer 456 on the open field lines 452 just outside the separatrix451. The edge layer 456 coalesces into jets 454 beyond the FRC length,providing a natural divertor.

The main magnetic system 410 includes a series of quasi-dc coils 412,414, and 416 that are situated at particular axial positions along thecomponents, i.e., along the confinement chamber 100, the formationsections 200 and the divertors 300, of the FRC system 10. The quasi-dccoils 412, 414 and 416 are fed by quasi-dc switching power supplies andproduce basic magnetic bias fields of about 0.1 T in the confinementchamber 100, the formation sections 200 and the divertors 300. Inaddition to the quasi-dc coils 412, 414 and 416, the main magneticsystem 410 includes quasi-dc mirror coils 420 (fed by switchingsupplies) between either end of the confinement chamber 100 and theadjacent formation sections 200. The quasi-dc mirror coils 420 providemagnetic mirror ratios of up to 5 and can be independently energized forequilibrium shaping control. In addition, mirror plugs 440, arepositioned between each of the formation sections 200 and divertors 300.The mirror plugs 440 comprise compact quasi-dc mirror coils 430 andmirror plug coils 444. The quasi-dc mirror coils 430 include three coils432, 434 and 436 (fed by switching supplies) that produce additionalguide fields to focus the magnetic flux surfaces 455 towards the smalldiameter passage 442 passing through the mirror plug coils 444. Themirror plug coils 444, which wrap around the small diameter passage 442and are fed by LC pulsed power circuitry, produce strong magnetic mirrorfields of up to 4 T. The purpose of this entire coil arrangement is totightly bundle and guide the magnetic flux surfaces 455 andend-streaming plasma jets 454 into the remote chambers 310 of thedivertors 300. Finally, a set of saddle-coil “antennas” 460 (see FIG. 15) are located outside the confinement chamber 100, two on each side ofthe mid-plane, and are fed by dc power supplies. The saddle-coilantennas 460 can be configured to provide a quasi-static magnetic dipoleor quadrupole field of about 0.01 T for controlling rotationalinstabilities and/or electron current control. The saddle-coil antennas460 can flexibly provide magnetic fields that are either symmetric orantisymmetric about the machine’s midplane, depending on the directionof the applied currents.

Pulsed Power Formation Systems

The pulsed power formation systems 210 operate on a modified theta-pinchprinciple. There are two systems that each power one of the formationsections 200. FIGS. 4 through 6 illustrate the main building blocks andarrangement of the formation systems 210. The formation system 210 iscomposed of a modular pulsed power arrangement that consists ofindividual units (=skids) 220 that each energize a sub-set of coils 232of a strap assembly 230 (=straps) that wrap around the formation quartztubes 240. Each skid 220 is composed of capacitors 221, inductors 223,fast high current switches 225 and associated trigger 222 and dumpcircuitry 224. In total, each formation system 210 stores between350-400 kJ of capacitive energy, which provides up to 35 GW of power toform and accelerate the FRCs. Coordinated operation of these componentsis achieved via a state-of-the-art trigger and control system 222 and224 that allows synchronized timing between the formation systems 210 oneach formation section 200 and minimizes switching jitter to tens ofnanoseconds. The advantage of this modular design is its flexibleoperation: FRCs can be formed in-situ and then accelerated and injected(=static formation) or formed and accelerated at the same time (=dynamicformation).

Neutral Beam Injectors

Neutral atom beams 600 are deployed on the FRC system 10 to provideheating and current drive as well as to develop fast particle pressure.As shown in FIGS. 3A, 3B and 8 , the individual beam lines comprisingneutral atom beam injector systems 610 and 640 are located around thecentral confinement chamber 100 and inject fast particles tangentiallyto the FRC plasma (and perpendicular or at an angel normal to the majoraxis of symmetry in the central confinement vessel 100) with an impactparameter such that the target trapping zone lies well within theseparatrix 451 (see FIG. 2 ). Each injector system 610 and 640 iscapable of injecting up to 1 MW of neutral beam power into the FRCplasma with particle energies between 20 and 40 keV. The systems 610 and640 are based on positive ion multi-aperture extraction sources andutilize geometric focusing, inertial cooling of the ion extraction gridsand differential pumping. Apart from using different plasma sources, thesystems 610 and 640 are primarily differentiated by their physicaldesign to meet their respective mounting locations, yielding side andtop injection capabilities. Typical components of these neutral beaminjectors are specifically illustrated in FIG. 7 for the side injectorsystems 610. As shown in FIG. 7 , each individual neutral beam system610 includes an RF plasma source 612 at an input end (this issubstituted with an arc source in systems 640) with a magnetic screen614 covering the end. An ion optical source and acceleration grids 616is coupled to the plasma source 612 and a gate valve 620 is positionedbetween the ion optical source and acceleration grids 616 and aneutralizer 622. A deflection magnet 624 and an ion dump 628 are locatedbetween the neutralizer 622 and an aiming device 630 at the exit end. Acooling system comprises two cryo-refrigerators 634, two cryopanels 636and a LN2 shroud 638. This flexible design allows for operation over abroad range of FRC parameters.

An alternative configuration for the neutral atom beam injectors 600 isthat of injecting the fast particles tangentially to the FRC plasma, butwith an angle A less than 90° relative to the major axis of symmetry inthe central confinement vessel 100. These types of orientation of thebeam injectors 615 are shown in FIG. 3C. In addition, the beam injectors615 may be oriented such that the beam injectors 615 on either side ofthe mid-plane of the central confinement vessel 100 inject theirparticles towards the mid-plane. Finally, the axial position of thesebeam systems 600 may be chosen closer to the mid-plane. Thesealternative injection embodiments facilitate a more central fuelingoption, which provides for better coupling of the beams and highertrapping efficiency of the injected fast particles. Furthermore,depending on the angle and axial position, this arrangement of the beaminjectors 615 allows more direct and independent control of the axialelongation and other characteristics of the FRC 450. For instance,injecting the beams at a shallow angle A relative to the vessel’s majoraxis of symmetry will create an FRC plasma with longer axial extensionand lower temperature while picking a more perpendicular angle A willlead to an axially shorter but hotter plasma. In this fashion theinjection angle A and location of the beam injectors 615 can beoptimized for different purposes. In addition, such angling andpositioning of the beam injectors 615 can allow beams of higher energy(which is generally more favorable for depositing more power with lessbeam divergence) to be injected into lower magnetic fields than wouldotherwise be necessary to trap such beams. This is due to the fact thatit is the azimuthal component of the energy that determines fast ionorbit scale (which becomes progressively smaller as the injection anglerelative to the vessel’s major axis of symmetry is reduced at constantbeam energy). Furthermore, angled injection towards the mid-plane andwith axial beam positions close to the mid-plane improves beam-plasmacoupling, even as the FRC plasma shrinks or otherwise axially contractsduring the injection period.

Turning to FIGS. 3D and 3E, another alternative configuration of the FRCsystem 10 includes inner divertors 302 in addition to the angled beaminjectors 615. The inner divertors 302 are positioned between theformation sections 200 and the confinement chamber 100, and areconfigured and operate substantially similar to the outer divertors 300.The inner divertors 302, which include fast switching magnetic coilstherein, are effectively inactive during the formation process to enablethe formation FRCs to pass through the inner divertors 302 as theformation FRCs translate toward the mid-plane of the confinement chamber100. Once the formation FRCs pass through the inner divertors 302 intothe confinement chamber 100, the inner divertors are activated tooperate substantially similar to the outer divertors and isolate theconfinement chamber 100 from the formation sections 200.

Pellet Injector

To provide a means to inject new particles and better control FRCparticle inventory, a 12-barrel pellet injector 700 (see e.g. I. Vinyaret al., “Pellet Injectors Developed at PELIN for JET, TAE, and HL-2A,”Proceedings of the 26^(th) Fusion Science and Technology Symposium,09/27 to 10/01 (2010)) is utilized on FRC system 10. FIG. 3 illustratesthe layout of the pellet injector 700 on the FRC system 10. Thecylindrical pellets (D ~ 1 mm, L ~ 1 - 2 mm) are injected into the FRCwith a velocity in the range of 150 - 250 km/s. Each individual pelletcontains about 5×10¹⁹ hydrogen atoms, which is comparable to the FRCparticle inventory.

Gettering Systems

It is well known that neutral halo gas is a serious problem in allconfinement systems. The charge exchange and recycling (release of coldimpurity material from the wall) processes can have a devastating effecton energy and particle confinement. In addition, any significant densityof neutral gas at or near the edge will lead to prompt losses of or atleast severely curtail the lifetime of injected large orbit (highenergy) particles (large orbit refers to particles having orbits on thescale of the FRC topology or at least orbit radii much larger than thecharacteristic magnetic field gradient length scale) - a fact that isdetrimental to all energetic plasma applications, including fusion viaauxiliary beam heating.

Surface conditioning is a means by which the detrimental effects ofneutral gas and impurities can be controlled or reduced in a confinementsystem. To this end the FRC system 10 provided herein employs Titaniumand Lithium deposition systems 810 and 820 that coat the plasma facingsurfaces of the confinement chamber (or vessel) 100 and divertors 300and 302 with films (tens of micrometers thick) of Ti and/or Li. Thecoatings are achieved via vapor deposition techniques. Solid Li and/orTi are evaporated and/or sublimated and sprayed onto nearby surfaces toform the coatings. The sources are atomic ovens with guide nozzles (incase of Li) 822 or heated spheres of solid with guide shrouding (in caseof Ti) 812. Li evaporator systems typically operate in a continuous modewhile Ti sublimators are mostly operated intermittently in betweenplasma operation. Operating temperatures of these systems are above 600°C. to obtain fast deposition rates. To achieve good wall coverage,multiple strategically located evaporator/sublimator systems arenecessary. FIG. 9 details a preferred arrangement of the getteringdeposition systems 810 and 820 in the FRC system 10. The coatings act asgettering surfaces and effectively pump atomic and molecular hydrogenicspecies (H and D). The coatings also reduce other typical impuritiessuch as carbon and oxygen to insignificant levels.

Mirror Plugs

As stated above, the FRC system 10 employs sets of mirror coils 420,430, and 444 as shown in FIGS. 2 and 3 . A first set of mirror coils 420is located at the two axial ends of the confinement chamber 100 and isindependently energized from the DC confinement, formation and divertorcoils 412, 414 and 416 of the main magnetic system 410. The first set ofmirror coils 420 primarily helps to steer and axially contain the FRC450 during merging and provides equilibrium shaping control duringsustainment. The first mirror coil set 420 produces nominally highermagnetic fields (around 0.4 to 0.5 T) than the central confinement fieldproduced by the central confinement coils 412. The second set of mirrorcoils 430, which includes three compact quasi-dc mirror coils 432, 434and 436, is located between the formation sections 200 and the divertors300 and are driven by a common switching power supply. The mirror coils432, 434 and 436, together with the more compact pulsed mirror plugcoils 444 (fed by a capacitive power supply) and the physicalconstriction 442 form the mirror plugs 440 that provide a narrow low gasconductance path with very high magnetic fields (between 2 to 4 T withrise times of about 10 to 20 ms). The most compact pulsed mirror coils444 are of compact radial dimensions, bore of 20 cm and similar length,compared to the meter-plus-scale bore and pancake design of theconfinement coils 412, 414 and 416. The purpose of the mirror plugs 440is multifold: (1) The coils 432, 434, 436 and 444 tightly bundle andguide the magnetic flux surfaces 452 and end-streaming plasma jets 454into the remote divertor chambers 300. This assures that the exhaustparticles reach the divertors 300 appropriately and that there arecontinuous flux surfaces 455 that trace from the open field line 452region of the central FRC 450 all the way to the divertors 300. (2) Thephysical constrictions 442 in the FRC system 10, through which that thecoils 432, 434, 436 and 444 enable passage of the magnetic flux surfaces452 and plasma jets 454, provide an impediment to neutral gas flow fromthe plasma guns 350 that sit in the divertors 300. In the same vein, theconstrictions 442 prevent back-streaming of gas from the formationsections 200 to the divertors 300 thereby reducing the number of neutralparticles that has to be introduced into the entire FRC system 10 whencommencing the startup of an FRC. (3) The strong axial mirrors producedby the coils 432, 434, 436 and 444 reduce axial particle losses andthereby reduce the parallel particle diffusivity on open field lines.

In the alternative configuration shown in FIGS. 3D and 3E, a set of lowprofile necking coils 421 are positions between the inner divertors 302and the formations sections 200.

Axial Plasma Guns

Plasma streams from guns 350 mounted in the divertor chambers 310 of thedivertors 300 are intended to improve stability and neutral beamperformance. The guns 350 are mounted on axis inside the chamber 310 ofthe divertors 300 as illustrated in FIGS. 3 and 10 and produce plasmaflowing along the open flux lines 452 in the divertor 300 and towardsthe center of the confinement chamber 100. The guns 350 operate at ahigh density gas discharge in a washer-stack channel and are designed togenerate several kiloamperes of fully ionized plasma for 5 to 10 ms. Theguns 350 include a pulsed magnetic coil that matches the output plasmastream with the desired size of the plasma in the confinement chamber100. The technical parameters of the guns 350 are characterized by achannel having a 5 to 13 cm outer diameter and up to about 10 cm innerdiameter and provide a discharge current of 10-15 kA at 400-600 V with agun-internal magnetic field of between 0.5 to 2.3 T.

The gun plasma streams can penetrate the magnetic fields of the mirrorplugs 440 and flow into the formation section 200 and confinementchamber 100. The efficiency of plasma transfer through the mirror plug440 increases with decreasing distance between the gun 350 and the plug440 and by making the plug 440 wider and shorter. Under reasonableconditions, the guns 350 can each deliver approximately 10²² protons/sthrough the 2 to 4 T mirror plugs 440 with high ion and electrontemperatures of about 150 to 300 eV and about 40 to 50 eV, respectively.The guns 350 provide significant refueling of the FRC edge layer 456,and an improved overall FRC particle confinement.

To further increase the plasma density, a gas box could be utilized topuff additional gas into the plasma stream from the guns 350. Thistechnique allows a several-fold increase in the injected plasma density.In the FRC system 10, a gas box installed on the divertor 300 side ofthe mirror plugs 440 improves the refueling of the FRC edge layer 456,formation of the FRC 450, and plasma line-tying.

Given all the adjustment parameters discussed above and also taking intoaccount that operation with just one or both guns is possible, it isreadily apparent that a wide spectrum of operating modes is accessible.

Biasing Electrodes

Electrical biasing of open flux surfaces can provide radial potentialsthat give rise to azimuthal E×B motion that provides a controlmechanism, analogous to turning a knob, to control rotation of the openfield line plasma as well as the actual FRC core 450 via velocity shear.To accomplish this control, the FRC system 10 employs various electrodesstrategically placed in various parts of the machine. FIG. 3 depictsbiasing electrodes positioned at preferred locations within the FRCsystem 10.

In principle, there are 4 classes of electrodes: (1) point electrodes905 in the confinement chamber 100 that make contact with particularopen field lines 452 in the edge of the FRC 450 to provide localcharging, (2) annular electrodes 900 between the confinement chamber 100and the formation sections 200 to charge far-edge flux layers 456 in anazimuthally symmetric fashion, (3) stacks of concentric electrodes 910in the divertors 300 to charge multiple concentric flux layers 455(whereby the selection of layers is controllable by adjusting coils 416to adjust the divertor magnetic field so as to terminate the desiredflux layers 456 on the appropriate electrodes 910), and finally (4) theanodes 920 (see FIG. 10 ) of the plasma guns 350 themselves (whichintercept inner open flux surfaces 455 near the separatrix of the FRC450). FIGS. 10 and 11 show some typical designs for some of these.

In all cases these electrodes are driven by pulsed or dc power sourcesat voltages up to about 800 V. Depending on electrode size and what fluxsurfaces are intersected, currents can be drawn in the kilo-ampererange.

Un-Sustained Operation of FRC System - Conventional Regime

The standard plasma formation on the FRC system 10 follows thewell-developed reversed-field-theta-pinch technique. A typical processfor starting up an FRC commences by driving the quasi-dc coils 412, 414,416, 420, 432, 434 and 436 to steady state operation. The RFTP pulsedpower circuits of the pulsed power formation systems 210 then drive thepulsed fast reversed magnet field coils 232 to create a temporaryreversed bias of about -0.05 T in the formation sections 200. At thispoint a predetermined amount of neutral gas at 9-20 psi is injected intothe two formation volumes defined by the quartz-tube chambers 240 of the(north and south) formation sections 200 via a set ofazimuthally-oriented puff-vales at flanges located on the outer ends ofthe formation sections 200. Next a small RF (~ hundreds of kilo-hertz)field is generated from a set of antennas on the surface of the quartztubes 240 to create pre-ionization in the form of local seed ionizationregions within the neutral gas columns. This is followed by applying atheta-ringing modulation on the current driving the pulsed fast reversedmagnet field coils 232, which leads to more global pre-ionization of thegas columns. Finally, the main pulsed power banks of the pulsed powerformation systems 210 are fired to drive pulsed fast reversed magnetfield coils 232 to create a forward-biased field of up to 0.4 T. Thisstep can be time-sequenced such that the forward-biased field isgenerated uniformly throughout the length of the formation tubes 240(static formation) or such that a consecutive peristaltic fieldmodulation is achieved along the axis of the formation tubes 240(dynamic formation).

In this entire formation process, the actual field reversal in theplasma occurs rapidly, within about 5 µs. The multi-gigawatt pulsedpower delivered to the forming plasma readily produces hot FRCs whichare then ejected from the formation sections 200 via application ofeither a time-sequenced modulation of the forward magnetic field(magnetic peristalsis) or temporarily increased currents in the lastcoils of coil sets 232 near the axial outer ends of the formation tubes210 (forming an axial magnetic field gradient that points axiallytowards the confinement chamber 100). The two (north and south)formation FRCs so formed and accelerated then expand into the largerdiameter confinement chamber 100, where the quasi-dc coils 412 produce aforward-biased field to control radial expansion and provide theequilibrium external magnetic flux.

Once the north and south formation FRCs arrive near the midplane of theconfinement chamber 100, the FRCs collide. During the collision theaxial kinetic energies of the north and south formation FRCs are largelythermalized as the FRCs merge ultimately into a single FRC 450. A largeset of plasma diagnostics are available in the confinement chamber 100to study the equilibria of the FRC 450. Typical operating conditions inthe FRC system 10 produce compound FRCs with separatrix radii of about0.4 m and about 3 m axial extend. Further characteristics are externalmagnetic fields of about 0.1 T, plasma densities around 5 x 10¹⁹ m⁻³ andtotal plasma temperature of up to 1 keV. Without any sustainment, i.e.,no heating and/or current drive via neutral beam injection or otherauxiliary means, the lifetime of these FRCs is limited to about 1 ms,the indigenous characteristic configuration decay time.

Experimental Data of Unsustained Operation - Conventional Regime

FIG. 12 shows a typical time evolution of the excluded flux radius,r_(ΔΦ), which approximates the separatrix radius, r_(s), to illustratethe dynamics of the theta-pinch merging process of the FRC 450. The two(north and south) individual plasmoids are produced simultaneously andthen accelerated out of the respective formation sections 200 at asupersonic speed, vz ~ 250 km/s, and collide near the midplane at z = 0.During the collision the plasmoids compress axially, followed by a rapidradial and axial expansion, before eventually merging to form an FRC450. Both radial and axial dynamics of the merging FRC 450 are evidencedby detailed density profile measurements and bolometer-based tomography.

Data from a representative un-sustained discharge of the FRC system 10are shown as functions of time in FIGS. 13A, 13B, 13C and 13D. The FRCis initiated at t = 0. The excluded flux radius at the machine’s axialmid-plane is shown in FIG. 13A. This data is obtained from an array ofmagnetic probes, located just inside the confinement chamber’s stainlesssteel wall, that measure the axial magnetic field. The steel wall is agood flux conserver on the time scales of this discharge.

Line-integrated densities are shown in FIG. 13B, from a 6-chordCO₂/He-Ne interferometer located at z = 0. Taking into account vertical(y) FRC displacement, as measured by bolometric tomography, Abelinversion yields the density contours of FIG. 13C. After some axial andradial sloshing during the first 0.1 ms, the FRC settles with a hollowdensity profile. This profile is fairly flat, with substantial densityon axis, as required by typical 2-D FRC equilibria.

Total plasma temperature is shown in FIG. 13D, derived from pressurebalance and fully consistent with Thomson scattering and spectroscopymeasurements.

Analysis from the entire excluded flux array indicates that the shape ofthe FRC separatrix (approximated by the excluded flux axial profiles)evolves gradually from racetrack to elliptical. This evolution, shown inFIG. 14 , is consistent with a gradual magnetic reconnection from two toa single FRC. Indeed, rough estimates suggest that in this particularinstant about 10% of the two initial FRC magnetic fluxes reconnectsduring the collision.

The FRC length shrinks steadily from 3 down to about 1 m during the FRClifetime. This shrinkage, visible in FIG. 14 , suggests that mostlyconvective energy loss dominates the FRC confinement. As the plasmapressure inside the separatrix decreases faster than the externalmagnetic pressure, the magnetic field line tension in the end regionscompresses the FRC axially, restoring axial and radial equilibrium. Forthe discharge discussed in FIGS. 13 and 14 , the FRC magnetic flux,particle inventory, and thermal energy (about 10 mWb, 7 x 10¹⁹particles, and 7 kJ, respectively) decrease by roughly an order ofmagnitude in the first millisecond, when the FRC equilibrium appears tosubside.

Sustained Operation - HPF Regime

The examples in FIGS. 12 to 14 are characteristic of decaying FRCswithout any sustainment. However, several techniques are deployed on theFRC system 10 to further improve FRC confinement (inner core and edgelayer) to the HPF regime and sustain the configuration.

Neutral Beams

First, fast (H) neutrals are injected perpendicular to B_(z) in beamsfrom the eight neutral beam injectors 600. The beams of fast neutralsare injected from the moment the north and south formation FRCs merge inthe confinement chamber 100 into one FRC 450. The fast ions, createdprimarily by charge exchange, have betatron orbits (with primary radiion the scale of the FRC topology or at least much larger than thecharacteristic magnetic field gradient length scale) that add to theazimuthal current of the FRC 450. After some fraction of the discharge(after 0.5 to 0.8 ms into the shot), a sufficiently large fast ionpopulation significantly improves the inner FRC’s stability andconfinement properties (see e.g. M. W. Binderbauer and N. Rostoker,Plasma Phys. 56, part 3, 451 (1996)). Furthermore, from a sustainmentperspective, the beams from the neutral beam injectors 600 are also theprimary means to drive current and heat the FRC plasma.

In the plasma regime of the FRC system 10, the fast ions slow downprimarily on plasma electrons. During the early part of a discharge,typical orbit-averaged slowing-down times of fast ions are 0.3 - 0.5 ms,which results in significant FRC heating, primarily of electrons. Thefast ions make large radial excursions outside of the separatrix becausethe internal FRC magnetic field is inherently low (about 0.03 T onaverage for a 0.1 T external axial field). The fast ions would bevulnerable to charge exchange loss, if the neutral gas density were toohigh outside of the separatrix. Therefore, wall gettering and othertechniques (such as the plasma gun 350 and mirror plugs 440 thatcontribute, amongst other things, to gas control) deployed on the FRCsystem 10 tend to minimize edge neutrals and enable the requiredbuild-up of fast ion current.

Pellet Injection

When a significant fast ion population is built up within the FRC 450,with higher electron temperatures and longer FRC lifetimes, frozen H orD pellets are injected into the FRC 450 from the pellet injector 700 tosustain the FRC particle inventory of the FRC 450. The anticipatedablation timescales are sufficiently short to provide a significant FRCparticle source. This rate can also be increased by enlarging thesurface area of the injected piece by breaking the individual pelletinto smaller fragments while in the barrels or injection tubes of thepellet injector 700 and before entering the confinement chamber 100, astep that can be achieved by increasing the friction between the pelletand the walls of the injection tube by tightening the bend radius of thelast segment of the injection tube right before entry into theconfinement chamber 100. By virtue of varying the firing sequence andrate of the 12 barrels (injection tubes) as well as the fragmentation,it is possible to tune the pellet injection system 700 to provide justthe desired level of particle inventory sustainment. In turn, this helpsmaintain the internal kinetic pressure in the FRC 450 and sustainedoperation and lifetime of the FRC 450.

Once the ablated atoms encounter significant plasma in the FRC 450, theybecome fully ionized. The resultant cold plasma component is thencollisionally heated by the indigenous FRC plasma. The energy necessaryto maintain a desired FRC temperature is ultimately supplied by the beaminjectors 600. In this sense the pellet injectors 700 together with theneutral beam injectors 600 form the system that maintains a steady stateand sustains the FRC 450.

CT Injector

As an alternative to the pellet injector, a compact toroid (CT) injectoris provided, mainly for fueling field-reversed configuration (FRCs)plasmas. The CT injector 720 comprises a magnetized coaxial plasma-gun(MCPG), which, as shown in FIGS. 22A and 22B, includes coaxialcylindrical inner and outer electrodes 722 and 724, a bias coilpositioned internal to the inner electrode 726 and an electrical break728 on an end opposite the discharge of the CT injector 720. Gas isinjected through a gas injection port 730 into a space between the innerand outer electrodes 722 and 724 and a Spheromak-like plasma isgenerated therefrom by discharge and pushed out from the gun by Lorentzforce. As shown in FIGS. 23A and 23B, a pair of CT injectors 720 arecoupled to the confinement vessel 100 near and on opposition sides ofthe mid-plane of the vessel 100 to inject CTs into the central FRCplasma within the confinement vessel 100. The discharge end of the CTinjectors 720 are directed towards the mid-plane of the confinementvessel 100 at an angel to the longitudinal axis of the confinementvessel 100 similar to the neutral beam injectors 615.

In an alternative embodiment, the CT injector 720, as shown in FIGS. 24Aand 24B, includes a drift tube 740 comprising an elongate cylindricaltube coupled to the discharge end of the CT injector 720. As depicted,the drift tube 740 includes drift tube coils 742 positioned about andaxially spaced along the tube. A plurality of diagnostic ports 744 aredepicted along the length of the tube.

The advantages of the CT injector 720 are: (1) control and adjustabilityof particle inventory per injected CT; (2) warm plasma is deposited(instead of cryogenic pellets); (3) system can be operated in rep-ratemode so as to allow for continuous fueling; (4) the system can alsorestore some magnetic flux as the injected CTs carry embedded magneticfield. In an embodiment for experimental use, the inner diameter of anouter electrode is 83.1 mm and the outer diameter of an inner electrodeis 54.0 mm. The surface of the inner electrode 722 is preferably coatedwith tungsten in order to reduce impurities coming out from theelectrode 722. As depicted, the bias coil 726 is mounted inside of theinner electrode 722.

In recent experiments a supersonic CT translation speed of up to ~100km/s was achieved. Other typical plasma parameters are as follows:electron density ~5 x 1021 m-3, electron temperature ~30-50 eV, andparticle inventory of -0.5-1.0x 1019. The high kinetic pressure of theCT allows the injected plasma to penetrate deeply into the FRC anddeposit the particles inside the separatrix. In recent experiments FRCparticle fueling has resulted in ~10-20% of the FRC particle inventorybeing provide by the CT injectors successfully demonstrating fueling canreadily be carried out without disrupting the FRC plasma.

Saddle Coils

To achieve steady state current drive and maintain the required ioncurrent it is desirable to prevent or significantly reduce electron spinup due to the electron-ion frictional force (resulting from collisionalion electron momentum transfer). The FRC system 10 utilizes aninnovative technique to provide electron breaking via an externallyapplied static magnetic dipole or quadrupole field. This is accomplishedvia the external saddle coils 460 depicted in FIG. 15 . The transverseapplied radial magnetic field from the saddle coils 460 induces an axialelectric field in the rotating FRC plasma. The resultant axial electroncurrent interacts with the radial magnetic field to produce an azimuthalbreaking force on the electrons, F_(θ)=-σV_(eθ)<|B_(r)|²>. For typicalconditions in the FRC system 10, the required applied magnetic dipole(or quadrupole) field inside the plasma needs to be only of order 0.001T to provide adequate electron breaking. The corresponding externalfield of about .015 T is small enough to not cause appreciable fastparticle losses or otherwise negatively impact confinement. In fact, theapplied magnetic dipole (or quadrupole) field contributes to suppressinstabilities. In combination with tangential neutral beam injection andaxial plasma injection, the saddle coils 460 provide an additional levelof control with regards to current maintenance and stability.

Mirror Plugs

The design of the pulsed coils 444 within the mirror plugs 440 permitsthe local generation of high magnetic fields (2 to 4 T) with modest(about 100 kJ) capacitive energy. For formation of magnetic fieldstypical of the present operation of the FRC system 10, all field lineswithin the formation volume are passing through the constrictions 442 atthe mirror plugs 440, as suggested by the magnetic field lines in FIG. 2and plasma wall contact does not occur. Furthermore, the mirror plugs440 in tandem with the quasi-dc divertor magnets 416 can be adjusted soto guide the field lines onto the divertor electrodes 910, or flare thefield lines in an end cusp configuration (not shown). The latterimproves stability and suppresses parallel electron thermal conduction.

The mirror plugs 440 by themselves also contribute to neutral gascontrol. The mirror plugs 440 permit a better utilization of thedeuterium gas puffed in to the quartz tubes during FRC formation, as gasback-streaming into the divertors 300 is significantly reduced by thesmall gas conductance of the plugs (a meager 500 L/s). Most of theresidual puffed gas inside the formation tubes 210 is quickly ionized.In addition, the high-density plasma flowing through the mirror plugs440 provides efficient neutral ionization hence an effective gasbarrier. As a result, most of the neutrals recycled in the divertors 300from the FRC edge layer 456 do not return to the confinement chamber100. In addition, the neutrals associated with the operation of theplasma guns 350 (as discussed below) will be mostly confined to thedivertors 300.

Finally, the mirror plugs 440 tend to improve the FRC edge layerconfinement. With mirror ratios (plug/confinement magnetic fields) inthe range 20 to 40, and with a 15 m length between the north and southmirror plugs 440, the edge layer particle confinement time τ_(||)increases by up to an order of magnitude. Improving τ_(||) readilyincreases the FRC particle confinement.

Assuming radial diffusive (D) particle loss from the separatrix volume453 balanced by axial loss (τ_(||)) from the edge layer 456, one obtains(2πr_(s)L_(s))(Dn_(s)/δ) = (2πr_(s)L_(sδ))(n_(s)/τ_(||)), from which theseparatrix density gradient length can be rewritten as δ =(Dτ_(||))^(½). Here r_(s), L_(s) and n_(s) are separatrix radius,separatrix length and separatrix density, respectively. The FRC particleconfinement time is τ_(N) = [πr_(s)²L_(s)<n>]/[(2πr_(s)L_(s))(Dn_(s)/δ)] = (<n>/n_(s))(τ_(⊥)τ_(||))^(½),where τ_(⊥)= a²/D with a=r_(s)/4. Physically, improving τ_(||) leads toincreased δ (reduced separatrix density gradient and drift parameter),and, therefore, reduced FRC particle loss. The overall improvement inFRC particle confinement is generally somewhat less than quadraticbecause n_(s) increases with τ_(||).

A significant improvement in τ_(||) also requires that the edge layer456 remains grossly stable (i.e., no n = 1 flute, firehose, or other MHDinstability typical of open systems). Use of the plasma guns 350provides for this preferred edge stability. In this sense, the mirrorplugs 440 and plasma gun 350 form an effective edge control system.

Plasma Guns

The plasma guns 350 improve the stability of the FRC exhaust jets 454 byline-tying. The gun plasmas from the plasma guns 350 are generatedwithout azimuthal angular momentum, which proves useful in controllingFRC rotational instabilities. As such the guns 350 are an effectivemeans to control FRC stability without the need for the older quadrupolestabilization technique. As a result, the plasma guns 350 make itpossible to take advantage of the beneficial effects of fast particlesor access the advanced hybrid kinetic FRC regime as outlined in thisdisclosure. Therefore, the plasma guns 350 enable the FRC system 10 tobe operated with saddle coil currents just adequate for electronbreaking but below the threshold that would cause FRC instability and/orlead to dramatic fast particle diffusion.

As mentioned in the Mirror Plug discussion above, if τ_(||) can besignificantly improved, the supplied gun plasma would be comparable tothe edge layer particle loss rate (~ 10²² /s). The lifetime of thegun-produced plasma in the FRC system 10 is in the millisecond range.Indeed, consider the gun plasma with density n_(e) ~ 10¹³ cm⁻³ and iontemperature of about 200 eV, confined between the end mirror plugs 440.The trap length L and mirror ratio R are about 15 m and 20,respectively. The ion mean free path due to Coulomb collisions is λ_(ii)~ 6x10³ cm and, since λ_(ii)lnR/R < L, the ions are confined in thegas-dynamic regime. The plasma confinement time in this regime is τ_(gd)~ RL/2V_(s)~ 2 ms, where V_(s) is the ion sound speed. For comparison,the classical ion confinement time for these plasma parameters would beτ_(c) ~ 0.5τ_(ii)(lnR + (lnR)^(0.5)) ~0.7 ms. The anomalous transversediffusion may, in principle, shorten the plasma confinement time.However, in the FRC system 10, if we assume the Bohm diffusion rate, theestimated transverse confinement time for the gun plasma is τ_(⊥) >τ_(gd)∼ 2 ms. Hence, the guns would provide significant refueling of theFRC edge layer 456, and an improved overall FRC particle confinement.

Furthermore, the gun plasma streams can be turned on in about 150 to 200microseconds, which permits use in FRC start-up, translation, andmerging into the confinement chamber 100. If turned on around t ∼ 0 (FRCmain bank initiation), the gun plasmas help to sustain the presentdynamically formed and merged FRC 450. The combined particle inventoriesfrom the formation FRCs and from the guns is adequate for neutral beamcapture, plasma heating, and long sustainment. If turned on at t in therange -1 to 0 ms, the gun plasmas can fill the quartz tubes 210 withplasma or ionize the gas puffed into the quartz tubes, thus permittingFRC formation with reduced or even perhaps zero puffed gas. The lattermay require sufficiently cold formation plasma to permit fast diffusionof the reversed bias magnetic field. If turned on at t < -2 ms, theplasma streams could fill the about 1 to 3 m³ field line volume of theformation and confinement regions of the formation sections 200 andconfinement chamber 100 with a target plasma density of a few 10¹³ cm⁻³,sufficient to allow neutral beam build-up prior to FRC arrival. Theformation FRCs could then be formed and translated into the resultingconfinement vessel plasma. In this way the plasma guns 350 enable a widevariety of operating conditions and parameter regimes.

Electrical Biasing

Control of the radial electric field profile in the edge layer 456 isbeneficial in various ways to FRC stability and confinement. By virtueof the innovative biasing components deployed in the FRC system 10 it ispossible to apply a variety of deliberate distributions of electricpotentials to a group of open flux surfaces throughout the machine fromareas well outside the central confinement region in the confinementchamber 100. In this way radial electric fields can be generated acrossthe edge layer 456 just outside of the FRC 450. These radial electricfields then modify the azimuthal rotation of the edge layer 456 andeffect its confinement via ExB velocity shear. Any differential rotationbetween the edge layer 456 and the FRC core 453 can then be transmittedto the inside of the FRC plasma by shear. As a result, controlling theedge layer 456 directly impacts the FRC core 453. Furthermore, since thefree energy in the plasma rotation can also be responsible forinstabilities, this technique provides a direct means to control theonset and growth of instabilities. In the FRC system 10, appropriateedge biasing provides an effective control of open field line transportand rotation as well as FRC core rotation. The location and shape of thevarious provided electrodes 900, 905, 910 and 920 allows for control ofdifferent groups of flux surfaces 455 and at different and independentpotentials. In this way a wide array of different electric fieldconfigurations and strengths can be realized, each with differentcharacteristic impact on plasma performance.

A key advantage of all these innovative biasing techniques is the factthat core and edge plasma behavior can be affected from well outside theFRC plasma, i.e. there is no need to bring any physical components intouch with the central hot plasma (which would have severe implicationsfor energy, flux and particle losses). This has a major beneficialimpact on performance and all potential applications of the HPF concept.

Experimental Data - HPF Operation

Injection of fast particles via beams from the neutral beam guns 600plays an important role in enabling the HPF regime. FIGS. 16A, 16B, 16Cand 16D illustrate this fact. Depicted is a set of curves showing howthe FRC lifetime correlates with the length of the beam pulses. Allother operating conditions are held constant for all dischargescomprising this study. The data is averaged over many shots and,therefore, represents typical behavior. It is clearly evident thatlonger beam duration produces longer lived FRCs. Looking at thisevidence as well as other diagnostics during this study, it demonstratesthat beams increase stability and reduce losses. The correlation betweenbeam pulse length and FRC lifetime is not perfect as beam trappingbecomes inefficient below a certain plasma size, i.e., as the FRC 450shrinks in physical size not all of the injected beams are interceptedand trapped. Shrinkage of the FRC is primarily due to the fact that netenergy loss (~ 4 MW about midway through the discharge) from the FRCplasma during the discharge is somewhat larger than the total power fedinto the FRC via the neutral beams (~2.5 MW) for the particularexperimental setup. Locating the beams at a location closer to themid-plane of the vessel 100 would tend to reduce these losses and extendFRC lifetime.

FIGS. 17A, 17B, 17C and 17D illustrate the effects of differentcomponents to achieve the HPF regime. It shows a family of typicalcurves depicting the lifetime of the FRC 450 as a function of time. Inall cases a constant, modest amount of beam power (about 2.5 MW) isinjected for the full duration of each discharge. Each curve isrepresentative of a different combination of components. For example,operating the FRC system 10 without any mirror plugs 440, plasma guns350 or gettering from the gettering systems 800 results in rapid onsetof rotational instability and loss of the FRC topology. Adding only themirror plugs 440 delays the onset of instabilities and increasesconfinement. Utilizing the combination of mirror plugs 440 and a plasmagun 350 further reduces instabilities and increases FRC lifetime.Finally adding gettering (Ti in this case) on top of the gun 350 andplugs 440 yields the best results - the resultant FRC is free ofinstabilities and exhibits the longest lifetime. It is clear from thisexperimental demonstration that the full combination of componentsproduces the best effect and provides the beams with the best targetconditions.

As shown in FIG. 1 , the newly discovered HPF regime exhibitsdramatically improved transport behavior. FIG. 1 illustrates the changein particle confinement time in the FRC system 10 between theconventionally regime and the HPF regime. As can be seen, it hasimproved by well over a factor of 5 in the HPF regime. In addition, FIG.1 details the particle confinement time in the FRC system 10 relative tothe particle confinement time in prior conventional FRC experiments.With regards to these other machines, the HPF regime of the FRC system10 has improved confinement by a factor of between 5 and close to 20.Finally, and most importantly, the nature of the confinement scaling ofthe FRC system 10 in the HPF regime is dramatically different from allprior measurements. Before the establishment of the HPF regime in theFRC system 10, various empirical scaling laws were derived from data topredict confinement times in prior FRC experiments. All those scalingrules depend mostly on the ratio R²/ρ_(i), where R is the radius of themagnetic field null (a loose measure of the physical scale of themachine) and ρ_(i) is the ion larmor radius evaluated in the externallyapplied field (a loose measure of the applied magnetic field). It isclear from FIG. 1 that long confinement in conventional FRCs is onlypossible at large machine size and/or high magnetic field. Operating theFRC system 10 in the conventional FRC regime CR tends to follow thosescaling rules, as indicated in FIG. 1 . However, the HPF regime isvastly superior and shows that much better confinement is attainablewithout large machine size or high magnetic fields. More importantly, itis also clear from FIG. 1 that the HPF regime results in improvedconfinement time with reduced plasma size as compared to the CR regime.Similar trends are also visible for flux and energy confinement times,as described below, which have increased by over a factor of 3-8 in theFRC system 10 as well. The breakthrough of the HPF regime, therefore,enables the use of modest beam power, lower magnetic fields and smallersize to sustain and maintain FRC equilibria in the FRC system 10 andfuture higher energy machines. Hand-in-hand with these improvementscomes lower operating and construction costs as well as reducedengineering complexity.

For further comparison, FIGS. 18A, 18B, 18C and 18D show data from arepresentative HPF regime discharge in the FRC system 10 as a functionof time. FIG. 18A depicts the excluded flux radius at the mid-plane. Forthese longer timescales the conducting steel wall is no longer as good aflux conserver and the magnetic probes internal to the wall areaugmented with probes outside the wall to properly account for magneticflux diffusion through the steel. Compared to typical performance in theconventional regime CR, as shown in FIGS. 13A, 13B, 13C and 13D, the HPFregime operating mode exhibits over 400% longer lifetime.

A representative cord of the line integrated density trace is shown inFIG. 18B with its Abel inverted complement, the density contours, inFIG. 18C. Compared to the conventional FRC regime CR, as shown in FIGS.13A, 13B, 13C and 13D, the plasma is more quiescent throughout thepulse, indicative of very stable operation. The peak density is alsoslightly lower in HPF shots - this is a consequence of the hotter totalplasma temperature (up to a factor of 2) as shown in FIG. 18D.

For the respective discharge illustrated in FIGS. 18A, 18B, 18C and 18D,the energy, particle and flux confinement times are 0.5 ms, 1 ms and 1ms, respectively. At a reference time of 1 ms into the discharge, thestored plasma energy is 2 kJ while the losses are about 4 MW, makingthis target very suitable for neutral beam sustainment.

FIG. 19 summarizes all advantages of the HPF regime in the form of anewly established experimental HPF flux confinement scaling. As can beseen in FIG. 19 , based on measurements taken before and after t = 0.5ms, i.e., t ≤ 0.5 ms and t > 0.5 ms, the flux confinement (andsimilarly, particle confinement and energy confinement) scales withroughly the square of the electron Temperature (T_(e)) for a givenseparatrix radius (r_(s)). This strong scaling with a positive power ofT_(e) (and not a negative power) is completely opposite to thatexhibited by conventional tokomaks, where confinement is typicallyinversely proportional to some power of the electron temperature. Themanifestation of this scaling is a direct consequence of the HPF stateand the large orbit (i.e. orbits on the scale of the FRC topology and/orat least the characteristic magnetic field gradient length scale) ionpopulation. Fundamentally, this new scaling substantially favors highoperating temperatures and enables relatively modest sized reactors.

With the advantages the HPF regime presents, FRC sustainment or steadystate driven by neutral beams is achievable, meaning global plasmaparameters such as plasma thermal energy, total particle numbers, plasmaradius and length as well as magnetic flux are sustainable at reasonablelevels without substantial decay. For comparison, FIG. 20 shows data inplot A from a representative HPF regime discharge in the FRC system 10as a function of time and in plot B for a projected representative HPFregime discharge in the FRC system 10 as a function of time where theFRC 450 is sustained without decay through the duration of the neutralbeam pulse. For plot A, neutral beams with total power in the range ofabout 2.5-2.9 MW were injected into the FRC 450 for an active beam pulselength of about 6 ms. The plasma diamagnetic lifetime depicted in plot Awas about 5.2 ms. More recent data shows a plasma diamagnetic lifetimeof about 7.2 ms is achievable with an active beam pulse length of about7 ms.

As noted above with regard to FIGS. 16A, 16B, 16C and 16D, thecorrelation between beam pulse length and FRC lifetime is not perfect asbeam trapping becomes inefficient below a certain plasma size, i.e., asthe FRC 450 shrinks in physical size not all of the injected beams areintercepted and trapped. Shrinkage or decay of the FRC is primarily dueto the fact that net energy loss (- 4 MW about midway through thedischarge) from the FRC plasma during the discharge is somewhat largerthan the total power fed into the FRC via the neutral beams (-2.5 MW)for the particular experimental setup. As noted with regard to FIG. 3C,angled beam injection from the neutral beam guns 600 towards themid-plane improves beam-plasma coupling, even as the FRC plasma shrinksor otherwise axially contracts during the injection period. In addition,appropriate pellet fueling will maintain the requisite plasma density.

Plot B is the result of simulations run using an active beam pulselength of about 6 ms and total beam power from the neutral beam guns 600of slightly more than about 10 MW, where neutral beams shall inject H(or D) neutrals with particle energy of about 15 keV. The equivalentcurrent injected by each of the beams is about 110 A. For plot B, thebeam injection angle to the device axis was about 20°, target radius0.19 m. Injection angle can be changed within the range 15° - 25°. Thebeams are to be injected in the co-current direction azimuthally. Thenet side force as well as net axial force from the neutral beam momentuminjection shall be minimized. As with plot A, fast (H) neutrals areinjected from the neutral beam injectors 600 from the moment the northand south formation FRCs merge in the confinement chamber 100 into oneFRC 450.

The simulations that where the foundation for plot B usemulti-dimensional hall-MHD solvers for the background plasma andequilibrium, fully kinetic Monte-Carlo based solvers for the energeticbeam components and all scattering processes, as well as a host ofcoupled transport equations for all plasma species to model interactiveloss processes. The transport components are empirically calibrated andextensively benchmarked against an experimental database.

As shown by plot B, the steady state diamagnetic lifetime of the FRC 450will be the length of the beam pulse. However, it is important to notethat the key correlation plot B shows is that when the beams are turnedoff the plasma or FRC begins to decay at that time, but not before. Thedecay will be similar to that which is observed in discharges which arenot beam-assisted - probably on order of 1 ms beyond the beam turn offtime - and is simply a reflection of the characteristic decay time ofthe plasma driven by the intrinsic loss processes.

Turning to FIGS. 21A, 21B, 21C, 21D and 21E, experiment resultsillustrated in the figures indicate achievement of FRC sustainment orsteady state driven by angled neutral beams, i.e., global plasmaparameters such as plasma radius, plasma density, plasma temperature aswell as magnetic flux are sustainable at constant levels without decayin correlation with NB pulse duration. For example, such plasmaparameters are essentially being kept constant for ~5+ ms. Such plasmaperformance, including the sustainment feature, has a strong correlationNB pulse duration, with diamagnetism persisting even severalmilliseconds after NB termination due to the accumulated fast ions. Asillustrated, the plasma performance is only limited by the pulse-lengthconstraints arising from finite stored energies in the associated powersupplies of many critical systems, such as the NB injectors as well asother system components.

Multi-Scaled Capture Type Vacuum Pumps

As noted above with regard to FIGS. 3A, 3B, 3C, 3D, 3E and 8 , theneutral atom beams 600 are deployed on the FRC system 10 to provideheating and current drive as well as to develop fast particle pressure.The individual beam lines comprising neutral atom beam injector systems600 are located around the central confinement chamber 100 and, as shownin FIGS. 3C, 3D and 3E, are preferably angled to inject neutralparticles towards the mid-plane of the confinement chamber 100. Toramp-up plasma temperatures and elevate system energies, the present FRCsystem 10 includes a neutral beam injector (NBI) system 600 of elevatedpower and expanded pulse length, e.g., for exemplary purposes only,power of about 20+ MW with up to 30 ms pulse length.

To further improve FRC sustainment and demonstrate FRC ramp-up to highplasma temperatures and elevated system energies, the present FRC system10 also includes multi-scaled capture type vacuum pumps in the outer andinner divertors 300 and 302 to prevent the buildup of neutralized gas inthe divertors 300 and 302. As illustrated in FIG. 25 , through variousmechanisms, charged plasma particles (such as, e.g., hydrogen anddeuterium) are lost, as indicated by arrows A, from the interior or core453 of the FRC plasma 450 to the open field line plasma. From there, thecharged particles flow, as indicated by arrows B, along the openmagnetic field lines 452 out of the central confinement vessel 100 toeach of the four divertors 300 and 302 on either side of the confinementvessel 100.

Once in the divertors 300 and 302, the charged particles will hitsurfaces within the divertor chambers 310, such as, e.g., biaselectrodes 910 in divertors 300 and 302 (FIGS. 3A, 3D, 10 and 26 ),become neutralized and come off as neutralized gas. Keeping the densityof such neutralized gas sufficiently low is necessary for FRCsustainment and ramp-up to high plasma temperatures and elevated systemenergies because electrons in the plasma along the open field lines 452will ionize the neutral gas in the divertors 300 and 302 and, thus, loseenergy (cooling) in the process. Electrons that are too cold causeexcessive drag on and slow down energetic ions orbiting around theplasma core of the FRC plasma 450. Below a predetermined neutral gasdensity, electron cooling from ionization tends not to be significant.

To avoid a buildup of such neutralized gas in the divertors 300 and 302,the neutralized gas must be pumped away to prevent the gas density levelN from exceeding a predetermined maximum level of Y, i.e., N < Y m⁻³.For example, in certain embodiments, this gas buildup cannot exceed thedensity level N of 10¹⁸ m⁻³ (3x10⁻⁵ Torr pressure equivalent at 300 K)in the inner divertors 302, and 2x10¹⁸ m⁻³ (6x10⁻⁵ Torr pressureequivalent at 300 K) in the outer divertors 300. The level of pumpingrequired to prevent exceeding this maximum density/pressure limit isdetermined by the rate of charged particles flowing into each of thefour divertors 300 and 302. The level of pumping required is analogousto pouring water into a leaky bucket having one or more holes. Thefaster water is poured into the bucket, the higher the level to whichthe water level rises. While the bigger the leak, i.e., the greater thesize and or number of holes, the lower the level to which the waterlevel drops. With a big enough leak (i.e., a pump) the water level(i.e., particle density/pressure) can be maintained below a water levellimit (i.e., a predetermined particle density/pressure limit; e.g.,about 10¹⁸ m⁻³) while water is poured into the bucket (i.e., chargeparticles flow into the divertors 300 and 302).

In operation of the present FRC system 10, as shown in FIG. 27 , all thecharged plasma particles flowing towards the divertors 300 and 302 areexpected to initially flow into the two outer divertors 300 with amaximum rate of about 1.25x10²² #/s, which in more familiar vacuum unitsis about 400 Torr-L/s. Embodiments of the present FRC system 10 areconfigured to change to magnetic fields shortly after FRC formation,e.g., within about 5 milliseconds, to switch 75% of the total particleflow from the outer divertors 300 to the inner divertors 302. Forexample, the initial flow rate into the inner divertors 302 will beabout 300 Torr-L/s. Within a short time, e.g., about 5-10 milliseconds,following the switching of particle flow from the outer divertors 300 tothe inner divertors 302, plasma confinement in the FRC 450 will improvesuch that the expected particle flow rates tend to drop down 4 to 5fold, e.g., down to about 60 Torr-L/s. A simple zero dimensionsimulation model showed that a combination of a 2 million L/s vacuumpump plus 15 m³ of volumetric pumping (letting gas expand into an emptyvolume) was required in each of the four divertors 300 and 302 to keepthe hydrogen gas density below preferred maximum limits. Deuteriumrequires 1.5 million L/s worth of pumping.

To handle these particles loads while keeping the gas density low enoughrequires an enormous amount of pumping. Conventional pumping solutionsare unable to provide the necessary amount of pumping within theconstraints associated with the divertors 300 and 302 of the present FRCsystem 10, which include but are not limited to, for example, cost, aswell as limited volumetric space (e.g., about 15 m³) and surface area(e.g., about 10 m²) inside each divertor 300 and 302.

The cheapest way to pump particles such as, e.g., hydrogen anddeuterium, is to use Titanium films deposited onto the surfaces of thechambers 310 of the divertors 300 and 302 to cause the particles tostick to the surfaces of the chambers 310 in the form a capture typevacuum pump (discussed in further detail below). About 2.2 L/cm²s ofpumping is achievable at room temperature, which corresponds to theprobability of the hydrogen particles sticking and being captured by thefilm of 5%. This is called the sticking factor, which can range from 0to 100%. Using a limited surface area of about 10 m² of area will onlyyield a total pump speed of 22,000 L/s at this sticking factor. Thispump speed is about 100 times less than what is required to handle theparticles loads of the present FRC system 10 while keeping the gasdensity below a predetermined maximum.

To meet the pumping needs of the present FRC system 10, a combination oftwo pumping solutions is employed. First, a titanium film is depositedon to cryogenically cooled surfaces, e.g., surfaces that arecryogenically cooled to about 77 K. Such cooling tends to increase thesticking factor up to about 4 fold, e.g., from about 5% to about 20%.Second, the pumping surfaces are configured into a plurality ofmulti-scaled self-similar surfaces to further increase the stickingfactor about 3 to 4 fold, e.g., from about 20% to about 70%. With suchincreases in sticking factor, a 100 fold increase in pump speed isachieved. For example, for hydrogen a pump speed of 2,400,000 L/s isachieved and for deuterium a pump speed of 1,500,000 L/s is achievedusing just 7.3 m² of the available surface area, which fits inside a 15m³ vacuum vessel of the divertors 300 and 302. These pumps can handlethe total amount of gas (capacity) generated from a plasma shot on thepresent FRC system 10. The pump keeps 95% of its pump speed from thisamount of gas, and can be regenerated to 100% by depositing moretitanium.

Capture Type Vacuum Pump

Gas molecules can be captured onto a surface of a flat plate 312 (FIG.28 ) by sticking to the surface of the plate 312. The capture of gasmolecules can happen via various physical processes such ascondensation, as well as physical or chemical adsorption onto surfacesthat can be composed of many different types of materials. Each time agas molecule hits this surface it can be captured with a probability ofsticking between 0 to 100%. This probability of sticking onto a flatsurface from a single hit to the surface is called the sticking factor(SF). If the gas molecule doesn’t stick it will typically leave thatsurface in a random direction according to the cosine law. The stickingfactor of a flat surface is independent of the size of the flat surface.However, a pump’s total pumping speed does depend on the surface area,sticking factor and average speed of the gas molecules, and is given byformula (1):

$Speed = \frac{1}{4}\left\langle v \right\rangle SF \times Area$

The effective sticking factor, and hence pump speed, can be increased bycombining two or more surfaces together such that the surfaces haveviews of each other. For example, as shown in FIG. 28 , five flat squareshaped walls 322, 324, 326, 328 and 325 can be combined to create fivesides of a cube 320 with one open side such that the internal surfacesof the walls 322, 324, 326, 328 and 325 have a view of each other. A gasmolecule entering into this cube 320 on the open side will hit one ofthe five surfaces and stick with a probability SF. If the gas moleculedoesn’t stick to the surface it initially hits, the gas molecule canhead back out of the open side of the cube 320 the gas molecule justentered from or the gas molecule can hit one of the other four surfacesof the cube 320 it has a view of with yet another chance of sticking toa surface by a probability of SF. A gas molecule can bounce aroundhitting the surfaces of the cube 320 many times before either stickingto one of the surfaces or leaving out through the open side of the cube320. This effectively increases the probably of a gas molecule stickingto a surface in the cube 320 compared to a flat square surface 312 ofthe same size as the opening of the cube 320. The cube 320 effectivelyequates to a flat surface 312, but has a higher effective SF than theflat surface 312 where the flat surface has the same area as the openside of the cube 320.

When combining two or more surfaces together such that the surfaces haveviews of each other, the resulting shape need not necessarily form theshape of a cube. The resultant shape can be any shape having multiplesurfaces that form more than just a flat surface such as an open sidedchamber, cavity or channel. For example, as shown in FIG. 29 , a boxwith a square opening like the cube 320 shown in FIG. 28 can be formedbut with a depth that varies. FIG. 29 provides a plot of the effectiveSF of the square opening of the box as a function of the Depth/Widthratio of the box for a given SF for flat surfaces that make up the box.A box with zero depth (Depth/Width = 0 too) is just a flat surface 312,so the effective SF will be the same as the given SF of the box’s flatsurfaces. Sample SFs for a flat surface are shown to include 0.05, 0.10,0.20 and 0.50. For a Depth/Width ratio of Depth/Width=1, the box 320(1)is a cube. Boxes 320(2), 320(3), 320(4) and 320(5) have Depth/Widthratios of 2:1, 3:1, 4:1 and 5:1, respectively.

In addition to the Depth/Width ratio being variable, the shape and thenumber of open sides may vary. The open sides need not to be square, butcan be any shape including, but not limited to, hexagonal, circular,rectangular, triangular, star, etc., as long as two or more internalsurfaces have a view of each other. The shape also doesn’t have to bemade of a number of discrete flat surfaces. It can be a continuouslycurved surface like a hemisphere. To calculate the effective SF for thehemisphere, the curved surface is assumed to be composed of an infinitenumber of infinitely small flat surfaces.

Self-Similar Surfaced Capture Pumps

One can take a basic shape to build self-similar structures on manyscale levels that will dramatically increase the effective SF. Forexample, the individual pump object in the form of the five sided cube320 described above (FIGS. 28 and 29 ), can be assembled with aplurality of cubes 320 into a 10x10 array of cubes to form a panel orwall 330. The array of cubes panel 330 can then be used to form the five(5) walls 342, 344, 345, 346 and 348 of a larger five (5) sided cube340.

This process can be replicated over and over again increasing the SF andhence pump’s speed and capacity. For example, as illustrated in FIGS. 31and 32 , if a flat square plate 312 having an SF of 5% is used to form afive sided cube 320, the SF of the opening of the cube 320 will increaseto 20%. The cube 320 can then be assembled with a plurality of cubes 320in a 10x10 array of cubes to form a “flat” square plane or wall 330 witha SF equal to 20%. If the array of cubes wall 330 having an SF of 20% isused to form a five sided cube 340, with sides 342, 344, 345, 346 and348, the SF of the opening of the cube 340 will increase to 50%. Thecube 340 can then be assembled with a plurality of cubes 340 in a 10x10array of cubes to form a “flat” square plane or wall 360 with a SF equalto 50%. If the array of cubes wall 360 having an SF of 50% is used toform a five sided cube 380, with sides 382, 384, 385, 386 and 388, theSF of the opening of the cube 380 will increase to 80%. This process canbe repeated as desired to reach an optimal SF level.

As shown in FIG. 26 , a plurality of the larger boxes 380 are positionedabout the interior of the chamber 310 of the divertors 300 and 302. Asshown in FIG. 31 and partially shown FIG. 26 , the box 380 is a fivesided cube formed by side and bottom plates 384 and 386 and opposingside and top plates extending at a first end of the side, bottom and topplates from an end plate 385. The box 380 having an opening opposite theend plate 385 at a second end of the side, bottom and top plates.

SF doesn’t depend on size. The increase of SF associated with the cubesof the previous example can achieved by cubes of the same size openingrather than making the opening larger. Stated differently, bytransitioning from configuration of the first cube 320 to theconfiguration of third cube 380 while keeping the opening of the firstand third cubes 320 and 380 the same size, a four-fold increase in SFand, hence, pump speed is achieved relative to the SF of a flat platecorresponding to the opening area. This is an example of discrete scalelevels of self-similarity. The first cube 320 is only a one scale cube,i.e., the internal surfaces of the walls of the cube 320 comprise flatsurfaces. However, the internal surfaces of the walls of the second cube340 are not flat but rather include an array of the first cubes 320.Similarly, the internal surfaces of the third cube 380 include an arrayof the second cubes 340.

As far as increasing the pump’s SF, speed and capacity, there is norequirement that the individual pump objects used to convert a flatsurface into a three (3) dimensional surface have to have the sameshapes or sizes. The individual pump objects just have to have a shapethat can increase the SF relative to a flat plate corresponding to theopening of the individual pump objects. In the examples provided above,a 10:1 ratio is used in the scale sizes of the self-similar cubes, butthis ratio can be anything. The number of scale levels, shape and sizecan be optimized per situation.

As was mentioned above, a combination of cryogenically cooled surfacesand self-similar shapes are employed in the present FRC system 10 toachieve a sticking factor of about 80% or above. In certain situations,the SF gets reduced down to 70% from some shields that prevent thetitanium from depositing out through the opening of the individualpumps.

There are ways to naturally produce these types of self-similarstructures. Titanium films grown on cryogenically cooled (77 K) surfaceunder different pressures of argon will produce sub-micron structuresthat exhibit self-similarity and will increase sticking factor of thesurface. However, the self-similar structures, such as, e.g., cubes 320,340 and 380, are purposely-engineered self-similar structures that arenot grown from deposited films but can be used in conjunction withdeposited films.

There are many other ways that gas can be trapped onto surfaces besidestitanium coatings. NEGs (Non-Evaporable Getters), cryogenically cooledactivated charcoal, are two of the more common.

NEGs (Non-Evaporable Getters) pumps are commonly used throughoutparticle accelerators. These are made from alloy powders mixtures ofTitanium, Vanadium, Aluminum, Zirconium, and Iron.

Typically, this NEG powder is sintered into disks that are arrangedspaced stacks, or onto metallic heater ribbon, which are then bent intoshapes. So they do employ shapes to increase the sticking factor, butonly at one scale level. They are not shaped into self-similarstructures on multi scale sizes. These NEG powders could be sinteredinto self-similar shaped structures to increase their low stickingfactors and hence pump speed without increasing the size of the pump.Increased NEG pump speed would help improve the vacuum performance ofparticle accelerators.

Activated charcoal cooled to 10 K can capture Hydrogen gas and cooledfurther to 4 K can capture Helium gas. It is one of the few ways to pumpHelium gas. It is used as a pump in fusion devices such as Tokamaks andNeutral Beams. Adhering a powdered activated charcoal onto aself-similar structure will increase the sticking factor and pumpspeeds.

According to an embodiment of the present disclosure, a method forgenerating and maintaining a magnetic field with a field reversedconfiguration (FRC) comprising forming an FRC about a plasma in aconfinement chamber, injecting a plurality of neutral beams into the FRCplasma at an angle toward the mid-plane of the confinement chamber,pumping neutralized gas molecules accumulating in first and seconddiametrically opposed divertors coupled to the confinement chamber withfirst and second capture vacuum pumps positioned in the first and seconddivertors and comprising two or more sides with surfaces having a viewof each other and an open side, wherein the first and second capturevacuum pumps having a sticking factor more than four (4) times greaterthan a sticking factor of a flat plate defining an area equivalent tothe open side of the first and second capture pumps.

According to a further embodiment of the present disclosure, at leastone of the two or more sides of the first and second capture vacuumpumps comprising an array of individual capture vacuum pumps.

According to a further embodiment of the present disclosure, each of theindividual capture vacuum pumps comprising two or more sides withsurfaces having a view of each other and an open side, wherein each ofthe individual capture vacuum pumps having a sticking factor greaterthan a sticking factor of a flat plate defining an area equivalent tothe open side of each of the individual capture vacuum pumps.

According to a further embodiment of the present disclosure, at leastone of the two or more sides of each of the individual capture vacuumpumps comprising a second array of individual capture vacuum pumps.

According to a further embodiment of the present disclosure, each of theindividual capture vacuum pumps of the second array comprising two ormore sides with surfaces having a view of each other and an open side,wherein each of the individual capture vacuum pumps of the second arrayhaving a sticking factor greater than a sticking factor of a flat platedefining an area equivalent to the open side of each of the individualcapture vacuum pumps of the second array.

According to a further embodiment of the present disclosure, the firstand second capture vacuum pumps having a sticking factor that is N timesgreater than a sticking factor of a flat plate defining an areaequivalent to the open side of the first and second capture pumps,wherein N is 4<N<16.

According to a further embodiment of the present disclosure, thesurfaces of the flat plate and the first and second vacuum pumpsincludes a film of titanium deposited thereon.

According to a further embodiment of the present disclosure, the methodfurther includes maintaining the FRC at or about a constant valuewithout decay by injecting beams of fast neutral atoms from neutral beaminjectors into the FRC plasma at an angle towards the mid through planeof the confinement chamber.

According to a further embodiment of the present disclosure, the methodfurther comprising generating a magnetic field within the confinementchamber with quasi dc coils extending about the confinement chamber anda mirror magnetic field within opposing ends of the confinement chamberwith quasi dc mirror coils extending about the opposing ends of theconfinement chamber.

According to a further embodiment of the present disclosure, the methodfurther comprising generating a magnetic field within the confinementchamber with quasi dc coils extending about the confinement chamber anda mirror magnetic field within opposing ends of the confinement chamberwith quasi dc mirror coils extending about the opposing ends of theconfinement chamber.

According to a further embodiment of the present disclosure, forming theFRC includes forming a formation FRC in opposing first and secondformation sections coupled to the confinement chamber and acceleratingthe formation FRC from the first and second formation sections towardsthe mid through plane of the confinement chamber where the two formationFRCs merge to form the FRC.

According to a further embodiment of the present disclosure, forming theFRC includes one of forming a formation FRC while accelerating theformation FRC towards the mid-plane of the confinement chamber andforming a formation FRC then accelerating the formation FRC towards themid through plane of the confinement chamber.

According to a further embodiment of the present disclosure,accelerating the formation FRC from the first and second formationsections towards the mid-plane of the confinement chamber includespassing the formation FRC from the first and second formation sectionsthrough first and second inner divertors coupled to opposite ends of theconfinement chamber interposing the confinement chamber and the firstand second formation sections.

According to a further embodiment of the present disclosure, passing theformation FRC from the first and second formation sections through firstand second inner divertors includes inactivating the first and secondinner divertors as the formation FRC from the first and second formationsections passes through the first and second inner divertors.

According to a further embodiment of the present disclosure, the methodfurther comprising guiding magnetic flux surfaces of the FRC into thefirst and second inner divertors.

According to a further embodiment of the present disclosure, the methodfurther comprising guiding magnetic flux surfaces of the FRC into firstand second outer divertors coupled to the ends of the formationsections.

According to a further embodiment of the present disclosure, the methodfurther comprising generating a magnetic field within the formationsections and the first and second outer divertors with quasi-dc coilsextending about the formation sections and divertors.

According to a further embodiment of the present disclosure, the methodfurther comprising generating a magnetic field within the formationsections and first and second inner divertors with quasi-dc coilsextending about the formation sections and divertors.

According to a further embodiment of the present disclosure, the methodfurther comprising generating a mirror magnetic field between the firstand second formation sections and the first and second outer divertorswith quasi-dc mirror coils.

According to a further embodiment of the present disclosure, the methodfurther comprising generating a mirror plug magnetic field within aconstriction between the first and second formation sections and thefirst and second outer divertors with quasi-dc mirror plug coilsextending about the constriction between the formation sections and thedivertors.

According to a further embodiment of the present disclosure, the methodfurther comprising generating a mirror magnetic field between theconfinement chamber and the first and second inner divertors withquasi-dc mirror coils and generating a necking magnetic field betweenthe first and second formation sections and the first and second innerdivertors with quasi-dc low profile necking coils.

According to a further embodiment of the present disclosure, the methodfurther comprising generating one of a magnetic dipole field and amagnetic quadrupole field within the chamber with saddle coils coupledto the chamber.

According to a further embodiment of the present disclosure, the methodfurther comprising conditioning the internal surfaces of the chamber andthe internal surfaces of first and second formation sections, first andsecond divertors interposing the confinement chamber and the first andsecond formation sections, and first and second outer divertors coupledto the first and second formation sections with a gettering system.

According to a further embodiment of the present disclosure, thegettering system includes one of a Titanium deposition system and aLithium deposition system.

According to a further embodiment of the present disclosure, the methodfurther comprising axially injecting plasma into the FRC from axiallymounted plasma guns.

According to a further embodiment of the present disclosure, the methodfurther comprising controlling the radial electric field profile in anedge layer of the FRC.

According to a further embodiment of the present disclosure, controllingthe radial electric field profile in an edge layer of the FRC includesapplying a distribution of electric potential to a group of open fluxsurfaces of the FRC with biasing electrodes.

According to a further embodiment of the present disclosure, the methodfurther comprising injecting compact toroid (CT) plasmas from first andsecond CT injectors into the FRC plasma at an angle towards themid-plane of the confinement chamber, wherein the first and second CTinjectors are diametrically opposed on opposing sides of the mid-planeof the confinement chamber.

According to a further embodiment of the present disclosure, a capturevacuum pump comprising two or more sides with surfaces having a view ofeach other and an open side, wherein capture vacuum pump having asticking factor more than four (4) times greater than a sticking factorof a flat plate defining an area equivalent to the open side of thecapture pump.

According to a further embodiment of the present disclosure, at leastone of the two or more sides of the first and second capture vacuumpumps comprising an array of individual capture vacuum pumps.

According to a further embodiment of the present disclosure, each of theindividual capture vacuum pumps comprising two or more sides withsurfaces having a view of each other and an open side, wherein each ofthe individual capture vacuum pumps having a sticking factor greaterthan a sticking factor of a flat plate defining an area equivalent tothe open side of each of the individual capture vacuum pumps.

According to a further embodiment of the present disclosure, at leastone of the two or more sides of each of the individual capture vacuumpumps comprising a second array of individual capture vacuum pumps.

According to a further embodiment of the present disclosure, each of theindividual capture vacuum pumps of the second array comprising two ormore sides with surfaces having a view of each other and an open side,wherein each of the individual capture vacuum pumps of the second arrayhaving a sticking factor greater than a sticking factor of a flat platedefining an area equivalent to the open side of each of the individualcapture vacuum pumps of the second array.

According to a further embodiment of the present disclosure, the firstand second capture vacuum pumps having a sticking factor that is N timesgreater than a sticking factor of a flat plate defining an areaequivalent to the open side of the first and second capture pumps,wherein N is 4<N<16.

According to a further embodiment of the present disclosure, thesurfaces of the flat plate and the first and second vacuum pumpsincludes a film of titanium deposited thereon.

According to a further embodiment of the present disclosure, a systemfor generating and maintaining a magnetic field with a field reversedconfiguration (FRC) comprising a confinement chamber, first and seconddiametrically opposed FRC formation sections coupled to the confinementchamber and including first and second capture vacuum pumps positionedwithin the first and second divertors and comprising two or more sideswith surfaces having a view of each other and an open side, wherein thefirst and second capture vacuum pumps having a sticking factor more thanfour (4) times greater than a sticking factor of a flat plate definingan area equivalent to the open side of the first and second capturepumps, one or more of a plurality of plasma guns, one or more biasingelectrodes and first and second mirror plugs, wherein the plurality ofplasma guns includes first and second axial plasma guns operably coupledto the first and second divertors, the first and second formationsections and the confinement chamber, wherein the one or more biasingelectrodes being positioned within one or more of the confinementchamber, the first and second formation sections, and the first andsecond outer divertors, and wherein the first and second mirror plugsbeing position between the first and second formation sections and thefirst and second divertors, a gettering system coupled to theconfinement chamber and the first and second divertors, a plurality ofneutral atom beam injectors coupled to the confinement chamber andangled toward a mid-plane of the confinement chamber.

According to a further embodiment of the present disclosure, the systemis configured to generate an FRC and maintain the FRC without decaywhile the neutral beams are injected into the.

According to a further embodiment of the present disclosure, the firstand second divertors comprise first and second inner divertorsinterposing the first and second formation sections and the confinementchamber, and further comprising first and second outer divertors coupledto the first and second formation sections, wherein the first and secondformation sections interposing the first and second inner divertors andthe first and second outer divertors.

According to a further embodiment of the present disclosure, the systemfurther comprising first and second axial plasma guns operably coupledto the first and second inner and outer divertors, the first and secondformation sections and the confinement chamber.

According to a further embodiment of the present disclosure, the systemfurther comprising two or more saddle coils coupled to the confinementchamber.

According to a further embodiment of the present disclosure, theformation section comprises modularized formation systems for generatingan FRC and translating it toward a midplane of the confinement chamber.

According to a further embodiment of the present disclosure, the biasingelectrodes includes one or more of one or more point electrodespositioned within the containment chamber to contact open field lines, aset of annular electrodes between the confinement chamber and the firstand second formation sections to charge far-edge flux layers in anazimuthally symmetric fashion, a plurality of concentric stackedelectrodes positioned in the first and second divertors to chargemultiple concentric flux layers, and anodes of the plasma guns tointercept open flux.

According to a further embodiment of the present disclosure, the systemfurther comprising first and second compact toroid (CT) injectorscoupled to the confinement chamber at an angle towards the mid-plane ofthe confinement chamber, wherein the first and second CT injectors arediametrically opposed on opposing sides of the mid-plane of theconfinement chamber.

The example embodiments provided herein, however, are merely intended asillustrative examples and not to be limiting in any way.

All features, elements, components, functions, and steps described withrespect to any embodiment provided herein are intended to be freelycombinable and substitutable with those from any other embodiment. If acertain feature, element, component, function, or step is described withrespect to only one embodiment, then it should be understood that thatfeature, element, component, function, or step can be used with everyother embodiment described herein unless explicitly stated otherwise.This paragraph therefore serves as antecedent basis and written supportfor the introduction of claims, at any time, that combine features,elements, components, functions, and steps from different embodiments,or that substitute features, elements, components, functions, and stepsfrom one embodiment with those of another, even if the followingdescription does not explicitly state, in a particular instance, thatsuch combinations or substitutions are possible. Express recitation ofevery possible combination and substitution is overly burdensome,especially given that the permissibility of each and every suchcombination and substitution will be readily recognized by those ofordinary skill in the art upon reading this description.

In many instances, entities are described herein as being coupled toother entities. It should be understood that the terms “coupled” and“connected” (or any of their forms) are used interchangeably herein and,in both cases, are generic to the direct coupling of two entities(without any non-negligible (e.g., parasitic) intervening entities) andthe indirect coupling of two entities (with one or more non-negligibleintervening entities). Where entities are shown as being directlycoupled together, or described as coupled together without descriptionof any intervening entity, it should be understood that those entitiescan be indirectly coupled together as well unless the context clearlydictates otherwise.

While the embodiments are susceptible to various modifications andalternative forms, specific examples thereof have been shown in thedrawings and are herein described in detail. It should be understood,however, that these embodiments are not to be limited to the particularform disclosed, but to the contrary, these embodiments are to cover allmodifications, equivalents, and alternatives falling within the spiritof the disclosure. Furthermore, any features, functions, steps, orelements of the embodiments may be recited in or added to the claims, aswell as negative limitations that define the inventive scope of theclaims by features, functions, steps, or elements that are not withinthat scope.

What is claimed is:
 1. A capture vacuum pump comprising an open sidedchamber comprising two or more plates with surfaces having a view ofeach other, the two or more plates comprising one or more side platescoupled to the end plate at a first end of the one or more side platesand extending to an opening defined by a second end of the one or moreside plates, the opening defining an area equivalent to the surface ofthe end plate with the length of the one or more side plates defining adepth (D) of the capture vacuum pump and the two or more plates withsurfaces having a view of the opening, a film of titanium deposited onthe surfaces of the plates, wherein the film deposited surfaces having asticking factor corresponding to the probability of an individual gasmolecule sticking to the film deposited surface due to a single hit ofthe individual gas molecule to the film deposited surface when the filmdeposited surfaces are exposed to the gas, wherein the capture vacuumpump has a sticking factor greater than a sticking factor of the filmdeposited surface of the end plate on its own.
 2. A capture vacuum pumpsystem comprising a first capture vacuum pump and a second capturevacuum pump, each of the first second capture vacuum pumps being acapture vacuum pump according to claim
 1. 3. The arrangement of claim 2, wherein at least one of the two or more plates of the first and secondcapture vacuum pumps comprise a first array of individual capture vacuumpumps, wherein each individual capture vacuum pump in the first array ofindividual capture vacuum pumps comprising two or more plates withsurfaces having a view of each other, the two or more plates comprisingone or more side plates coupled to an end plate at a first end of theone or more side plates and extending to an opening defined by a secondend of the one or more side plates, the opening defining an areaequivalent to the surface of the end plate with the length of the one ormore side plates defining a depth (D) of the individual capture vacuumpump, and the two or more plates with surfaces having a view of theopening.
 4. The arrangement of claim 3, wherein at least one of the twoor more plates of each individual capture vacuum pump in the array ofthe individual capture vacuum pumps comprising a second array ofindividual capture vacuum pumps, wherein each individual capture vacuumpump in the second array of individual capture vacuum pumps being acapture vacuum pump comprising two or more plates with surfaces having aview of each other, the two or more plates comprising one or more sideplates coupled to an end plate at a first end of the one or more sideplates and extending to an opening defined by a second end of the one ormore side plates, the opening defining an area equivalent to the surfaceof the end plate with the length of the one or more side plates defininga depth (D) of the individual capture vacuum pump, and the two or moreplates with surfaces having a view of the opening.
 5. The arrangementaccording to any one of claim 2, wherein the first and second capturevacuum pumps having a sticking factor that is N times greater than asticking factor of a flat plate defining an area equivalent to the openside of the first and second capture pumps, wherein N is 4<N<16.
 6. Thearrangement according to any one of claim 3, wherein the first andsecond capture vacuum pumps having a sticking factor that is N timesgreater than a sticking factor of a flat plate defining an areaequivalent to the open side of the first and second capture pumps,wherein N is 4<N<16.
 7. The arrangement according to any one of claim 4,wherein the first and second capture vacuum pumps having a stickingfactor that is N times greater than a sticking factor of a flat platedefining an area equivalent to the open side of the first and secondcapture pumps, wherein N is 4<N<16.
 8. The arrangement according to anyone of claim 2, wherein the film deposited surfaces of the end plate andthe first and second side plates includes a film of titanium depositedthereon.
 9. The arrangement according to any one of claim 3, wherein thefilm deposited surfaces of the end plate and the first and second sideplates includes a film of titanium deposited thereon.
 10. Thearrangement according to any one of claim 4, wherein the film depositedsurfaces of the end plate and the first and second side plates includesa film of titanium deposited thereon.